Electron multiplier discharge device



Dec. 2, 1941. G, B. BANKS 2,264,269

ELECTRON MULTIPLIER DISCHARGE DEVICE Filed July 15, 1938 INVENTORGEOKGEBAZDW/A/BAMKS'.

ATTORNEYS Patented Dec. 2, 1941 ELECTRON MULTIPLIER DISCHARGE DEVICEGeorge Baldwin Banks, Billerioay, England, assignor to Radio Corporationof America, a corporation of Delaware Application July 13, 1938, SerialNo. 218,982

In Great Britain July 15, 1937 l 11 Claims. (01. 250-175) This inventionrel-ates to electron discharge devices and more specifically to electrondischarge devices of the electron multiplier type, that is to sayelectron discharge devices of the kind wherein a primary electron streamis multiplied one or more times by secondary emission effects to producean amplified final electron current.

There are numerous known forms of electron multipliers but a commondifi'iculty presented by all known electron multipliers as at present inuse, is that the anode or output impedance is very high-approachinginfinity. This, of course, constitutes a serious practical limitationbecause the obtaining of substantial power output from an electrondischarge device involves that the load or utilization circuit bematched to the impedance of the said device, and if, as is the case withknown electron multipliers, the anode or output impedance approachesinfinity, it becomes practically impossible to match a loudspeaker, tankcircuit, or other ordinary load to the device.

The principal object of the present invention is to avoid thislimitation and to enable electron multipliers to be produced havingoutput or anode impedance of desired convenient values. As will be seenlater, the present invention enables electron multipliers to be madewith either positive or negative resistance characteristics. In general,however, the most important use of the invention will be to provideelectron multipliers of relatively low output impedance.

As is well known the ordinary known electron multiplier includes aprimary cathode source, a control electrode, a final output electrode,and in succession between said source and said output electrode one ormore similar secondary emissive electrodes which are substantiallyuniformly secondarily emissive over their whole operating surfaces.Electrons impinge on these emitters to release secondary electrons inmultiplied quantity, electrons from the primary cathode travelling tothe first secondary emitter electrode, secondary electrons from whichpass to the next secondary emitter electrode, and so on, until the finaloutput electrode is reached.

According to this invention at least the last secondary emitterelectrode (i. e. that electrode from which secondary electrons pass tothe final output electrode) is not made as has hitherto been usual ofsubstantially uniform secondary emitting qualities over its wholeoperating surface, but is made more highly secondarily emisof itssurface than elsewhere, the choice of the selected more highly emissivepart or parts being made in accordance with the operating characteristic required.

In order that the invention may be the better understood reference tothe drawing will be made, in which Figure 1 shows a known electronmultiplier for explaining the invention,

Fig. 2 shows graphically a representation between voltage and currentfor explaining the theory of operation of the invention;

Figs. 3 and 5 show electrode structures for use in the electronmultiplier, while Fig. 4 shows an embodiment of the invention utilizingthe new and improved form of electrodes.

In the known electron multiplier referred to and representedschematically in Figure 1 there is employed a primary cathode l, acontrol electrode la, a plurality of secondary emitter electrodes 2a,2b, 2c, 2d, a plurality of field electrodes 3, 3a, 3b, 3c, 3d and anoutput electrode 4. Input potentials to be amplified may be applied asindicated at Input between the electrodes l and la. The surface whichmay be regarded as the effective plane of emission of primary electrons,and the secondary emitter electrodes 2a to 2d lie substantially in lineand in one plane and the field electrodes 3 to 3d lie substantially inline and in a parallel plane, one field electrode 3 being opposite theprimary cathode l and each remaining field electrode 2a, 3b, 3c,-3d,being each opposite the corresponding secondary emitter electrode211,219, 20 or 2d. The output electrode 4 is in a plane at right anglesto thetwo parallel planes already mentioned, lying adjacent the lastfield electrode 3d and the last secondary emitter electrode 2d and alittle outwardly of the space between the two. In use the fieldelectrode 3 opposite the primary cathode I is connected to sive over apredetermined selected part or parts the first secondary emitterelectrode 2a, the next field electrode 3a is connected to the secondsecondary emitterelectrode 2b, and so on, increasing positive potentialsbeing supplied to successive secondary emitter electrodes and themaximum positive potential being applied to the output electrode. threadthe, space between the sheet of field electrodes and the sheet ofsecondary emitter electrodes, the whole arrangement being such that theelectrons travel (as indicated in broken lines) in more or lesscycloidal paths from the primary cathode I to the first secondaryemitter electrode 2a, thence to the second secondary A magnetic field isapplied to r for increasing values of output electrode voltage.

The useful portion of this characteristic curve is the substantiallyhorizontal portion XY which,

being substantially horizontal, represents anoutput impedance ofsubstantially infinity.

In accordance with this invention the above described known electronmultiplier 'is -m'o dified by making the final secondary emitterelectrode that is to say the electrode 2d which isnearest the outputelectrode-not of substantially uniform secondary emitting propertiesover-its whole surface, -'but much more highly secondary emitting overparts of its surfacethan over other parts.

Electrode 201 may be a composite electrode made partly of silver andpartly of some other metal so that when sensitized the emission from thesilver portion is considerably greater than from the other portion. Theelectrode 2d, which is assumed to be rectangular in shape as in theusual way, may be as shown in face view in the accompanying Figure 3-andhave its highly emissive portion -E2d (shown plain) of triangular formoccupying about half the surface of the whole electrode, this triangularhalf having its base along one edge of the-electrode and its apex at themiddle of the parallel edge so that there are left two areas N2d (shownshaded) of lower secondary electron emission said areas being rightangle triangles with their hypotenuses and apices meeting in that edgeofthe wholeplate in which is the apex of the highly emissive triangleE2d. Further the output electrode 4 and the last two field electrodes 303d instead of being separate and insulated from one another as shown inFigure l are connected together and preferably are integral with oneanother as shown in the accompanying Figure 4 where the compositeelectrode is marked 34. The separationbetween the portion of electrode34 opposite the last secondary emitter-electrode and the said lastsecondary emitter-electrode 2d is the same as that between electrodes 3and I; So and 2a.; and 3b and 222; but the portion-of the compositeelectrode 34 opposite the penultimate emitter electrode 20 'is madedouble that employed elsewhere, i. e. between 3 and l, 3a'and2a and3band 22). Thus in the integral construction of output electrode and last.two field electrodes illustrated these three electrodes are constitutedby a single plate 34 having three right angled bends in it, one endportion lying in a plane at right angles to two parallel planes in whichthe intermediate portion and the other end portion (these two portionsconstitutethe two field electrodes) lie. In use the usual magnetic fieldis applied and the voltage applied to the composite output electrode andlast two field electrodes ('34) exceeds that applied to the lastsecondary emitter electrode 2d by the same amount as that by which thelast mentioned voltage exceeds that applied to the penultimate secondaryemitter electrode 2c and to the field electrode 3b opposite the lastsecondary emitter but two (211-) As will be appreciated, the reason formaking the separation of the penultimate field electrode from itsopposite secondary emitter electrode twice the separation employedelsewhere is to enable the correct electrostatic field conditions to beobtained despite the fact that the last two field electrodes and theoutput electrodes are at the same voltage.

In the static condition the potential applied to the output electrode issuch that electrons take Lamean path and strike the last secondaryemitter electrode at its centre line, the secondary emissionobtained inthis condition being the mean .outputelectrode current. Under dynamiccon- .diti'ons the potential of the output electrode varies about themean value and the number of electrons released from the last secondaryemit- "ter electrode varies accordingly, for, under dynamic conditionsthe point of impact of electrons on the last secondary emitter electrodedepends on the output electrode voltage. If the said voltage is high thesubstantially cycloidal paths followed by electrons will be long andthey will fall on an area of high emissivity, if said voltage is low thepaths become shorter and areas of lower emissivity are struck.

'By suitably choosing the shape and disposition of the more highlyemissive portion or .portions of the last secondary emitter electrode 2dan output electrode current (In0rdinateS)-- output electrode voltage(VA-abscissae) curve like that shown by the curve B of Fig. '2 can beobtained this curve comprising a substantially straight rising line X'Y'representing a relatively low finite output impedance.

By differently choosing the arrangement and disposition of the morehighly emissive portion or portions of the last secondary emitterelectrode, other desired shapes of characteristic may be obtained. Forexample as shown in the accompanying Figure 5 by making the more highlyemissive portion E2d of trapezoidal shape with one of the two paralleledges constituted by one edge of the whole plate and the other lying inthe other (thus leaving two triangles NZd of low emission properties,one at each end) a higher output impedance may be obtained. Again, byreversing the form of final secondary emitter electrode illustrated inFigure 3, that'is to say, by making the triangular area 'E2d of Fig. 3of low emission and the triangularareas NW of Fig. 3 of high emission,-a negatively sloping characteristic may beobtained.

In experimental practice with a tube having a final emitter electrodeconstructed as represented in Fig. 3 an output impedance orcharacteristic slope of 15,000 ohms was obtained, a figure which is verymuch lower than is obtained with normal known electron multipliers.

Having now described my invention, what I claim is:

'1. An electron multiplier tube comprising a cathode, a controlelectrode, a first set and a second set of secondary electron emissiveplates, both of said sets being co-planar, a plurality of planarelectrodes each of said electrodes being parallel to and in registerwith one of theplates of said first set of plates, and-an outputelectrode positioned beyond said second set of plates, said outputelectrode having two faces parallel to and another face perpendicular tosaid second set of platesgthe surface of the plate of said second set ofplates nearest the perpendicular face of said of lower secondaryelectronemissivity than the emissivity of the. remaining portion'of said plate.

2. A tube comprising a'primary cathode, a control electrode, a series ofsecondary emitter electrodes co-planar with one another and withsaidprimary cathode, a plurality of field electrodes, one opposite theprimary cathode and one opposite each of the secondary emitterelectrodes, and an output electrode substantially at right angles to theplane of said secondary emitter electrodes, said output electrode beingat the end of said series remote from the primary cathode and betweensaid plane and a second plane which is parallel thereto all the fieldelectrodes except the last but one being in said second plane theseparation between said last but one field electrode and the secondaryemitter electrode opposite the same being substantially twice theseparation between the two said planes.

3. A tube comprising a primary cathode, a control electrode, a series ofsecondary emitter electrodes, a series of field electrodes, one adjacentthe primary cathode and. one adjacent each of the secondary emitterelectrodes, and an output electrode, the distance between thepenultimate field electrode and the secondary emitter electrode adjacentthereto being substantially twice the distance between any other fieldelectrode and its secondary emitter electrode therewith associated.

4. An electron multiplier tube comprising a cathode, a controlelectrode, a plurality of pairs of parallel plate electrodes, one plateof each pair being secondary electron emissive, said secondary electronemissive plates being coplanar, an electrode in register with saidcathode and said control electrode for directing electrons from thecathode onto one of said secondary electron emissive plates, a planarsecondary emissive cathode coplanar with and longitudinally displacedfrom said secondary electron emissive plates, a second planar secondaryelectron emissive electrode coplanar with said first named planarelectrode, said second planar electrode having a predetermined secondaryelectron emissivity over a predetermined area of the electrode and adifferent predetermined secondary emissivity over the remainder of thearea of the electrode, and an output electrode having both a faceparallel to and in register with each of the two planar secondaryemissive electrodes and a face perpendicular to the plane of said planarsecondary emissive electrodes.

5. An electron multiplier tube comprising a cathode, a controlelectrode, a plurality of pairs of parallel plate electrodes, one plateof each pair being secondary electron emissive, said secondary electronemissive plates being coplanar,

an electrode in register with said cathode and said control electrodefor directing electrons from the cathode onto one of said secondaryelectron emissive plates, a planar secondary emissive cathode coplanarwith and longitudinally displaced from said secondary electron emissiveplates, a rectangular secondary electron emissive planar electrodecoplanar with said first planar secondary emissive electrode, saidrectangular electrode having a triangular area of predeterminedsecondary electron emissivity and a different predetermined secondaryelectron emissivity over the remainder of the area of said electrode,and an output electrode having both a face parallel to and in registerwith each of the two planar secondary emissive electrodes and a faceperpendicular to the plane of said planar secondary emissive electrodes.

6. electron, multiplier tube comprising a cathode, a control electrode,a plurality of pairs of parallel plate electrodes, one plate of eachpair being secondary electron emissive, said secondary electron emissiveplates being coplanar, an electrode in register with said cathode andsaid control. electrode for directing electrons from the, cathode ontoone of said secondary electron emissive plates, a planar secondaryemissive cathode coplanar with and longitudinally displaced from saidsecondary electron emissive plates, a rectangular secondary electronemissive planar electrode coplanar with said first planar secondaryemissive electrode, said rectangular electrode having a trapezoidal areaof predetermined secondary electron emissivity and a differentpredetermined secondary electron emissivity over the remainder of thearea of said electrode, and an output electrode having both a faceparallel to and in register with each of the two planar secondaryemissive electrodes and a face perpendicular to the plane of said planarsecondary emissive electrodes.

7. An electron multiplier tube comprising a cathode, a controlelectrode, a first set and a second set of secondary electron emissiveplates, both of said sets being co-planar, a plurality of planarelectrodes each of said electrodes being parallel to and in registerwith one of the plates of said first set of plates, and an outputelectrode positioned beyond said second set of plates, said outputelectrode having two faces parallel to and another face perpendicular tosaid second set of plates.

8. An electron multiplier tube comprising a cathode, a controlelectrode, a first set and a second set of secondary electron emissiveplates, both of said sets being co-planar, a plurality of planarelectrodes, each of said electrodes being parallel to and in registerwith one of the plates of said first set of plates, a further electrodein register with said cathode and control electrode for directingelectrons from said cathode onto one of the plates of said first set ofplates, and an output electrode positioned beyond said second set ofplates, said output electrode having two faces parallel to and anotherface perpendicular to plates, said output electrode having two facesparallel to and another face perpendicular to said second set of plates,and potential supply leads connected to said cathode, said first set andsecond set of plates, and all of said electrodes.

10. An electron multiplier tube comprising a cathode, a controlelectrode, a first set and a second set of secondary electron emissiveplates, both of said sets being co-planar with the plates of said secondset being progressively longitudinally displaced from said first set,the furthest displaced plate of said second set having a highersecondary electron emissivity over a predetermined selected part of itssurface than the emissivity of the remaining part of its surface,thearea of the predetermined selected part varying progressively in thedirection of the longitudinal disond set :oflplates, said :outputelectrode having two :faces parallelto and-another face perpendicular tosaid furthest displaced plate.

11. A tube a's claimed in claim 10 wherein the 5 predeterminedselectedpart is of sensitized silver and the remaining part ofsaid electrode isof a different metal.

GEORGE BALDWIN BANKS.

